Refrigeration oil is a petroleum derivative consisting essentially of either naphthenic or paraffinic base oils which have been highly refined to remove impurities and high boiling fractions (including waxes).
Refrigeration oil must work over an extremely wide temperature range. For example, in a large industrial air conditioner used in an office building, the oil must work at a temperature as low as -50.degree. Fahrenheit (-46.degree. C.) without hardening or flocculating, and must work in temperatures as high as about 300.degree. F. (149.degree. C.) or more without decomposing substantially. This extremely wide temperature range is necessary because the refrigeration oil is alternately heated and cooled during the cycles of compression and expansion of the working fluid. Thus, one requirement for refrigeration oil is that it have a very low floc point, which can be as low as -65.degree. F. (-54.degree. C.) for some applications. Other applications, such as automotive air conditioners, are less critical and require a floc point of only about -15.degree. F. (-26.degree. C.).
Refrigeration oil also must be compatible with chlorofluorocarbon refrigerants, also called "working fluids" herein. In the presence of unstable oil or an instability-promoting additive, these working fluids generate hydrochloric acid. The free hydrochloric acid thus produced is consumed when it attacks ethylenic or aromatic unsaturation or compounds of nitrogen, oxygen, or sulfur in the refrigeration oil to promote sludge formation. Thus, refrigeration oil must be essentially free of either type of unsaturation, nitrogen, oxygen, and sulfur to prevent its decomposition at elevated temperatures in the presence of chlorofluorocarbon refrigerants.
Resistance of a selected chlorofluorocarbon refrigerant to decomposition in the presence of a selected refrigeration oil is measured by the sealed tube stability test. When measured as described below, the sealed tube stability value of the refrigeration oil should be no more than about one percent decomposition of FREON 12 refrigerant under the test conditions. ("FREON" is a trademark of E.I. du Pont de Nemours & Co., Wilmington, Delaware, for refrigerants. "FREON 12" is a trademark for dichlorodifluoromethane.)
The stability requirements of refrigeration oils are paramount. To avoid instability, formulations of refrigeration oils have avoided using the lubricity-improving additives which are commonly used in other types of lubricants. Kirk-Othmer Encyclopedia of Chemical Technology, 3d ed., Volume 14, page 486 (Table 3) states that no additives are commonly used in refrigeration oils.
A third requirement of refrigeration oils is that they should provide a consistently high level of lubricity to protect the working parts of the compressor.
A persistent problem in the art has been to find additives which will increase the lubricity of a refrigeration oil without sacrificing its low floc point and great resistance to decomposition.
U.S. Pat. No. 4,800,013, issued Jan. 24, 1989 (and therefore not prior art under 35 U.S.C. .sctn.102(b)), teaches a refrigeration oil composition comprising a mixture of a paraffin base oil and a naphthenic base oil. This reference discloses the production, and some of the characteristics required, of refrigeration oils according to the present invention. This patent does not disclose halogenated paraffins.
Elsey et al., "A Method Of Evaluating Refrigerator Oils", Refrigerating Engineering, July 1952, pages 737-742, discloses that refrigerants can react with petroleum-based lubricating oils to form acid gas and carbonaceous sludge. The chlorine from the halogenated refrigerant reacts with hydrogen from the hydrocarbon oil to carbonize and therefore degrade the oil. The reference discloses that the more chlorine the refrigerant contains, the more readily it reacts with hydrocarbons. Fluorine substituents on the refrigerant are recognized to increase the stability of the refrigerant.
Several references disclose the use of halogenated paraffin waxes or oils in compositions not used as refrigeration lubricants.
U.S. Pat. No. 3,085,868, issued to Champagnat on Apr. 16, 1963, discloses addition of a chlorinated mineral wax to a base oil to provide an improved petroleum fuel oil.
U.S. Pat. No. 4,010,107, issued to Rothert on Mar. 1, 1977, teaches a lubricating oil composition useful as an automobile transmission fluid. This lubricant comprises a base oil, various other ingredients, and a chlorinated olefin containing from about 15 to 50 carbon atoms and from 20% to about 60% by weight chlorine. The addition of the chlorinated olefin is taught to prevent or retard corrosion of metal parts of the transmission. The patent does not mention floc points at all. It is also not apparent whether the "chlorinated olefins" discussed in this patent have all their olefinic groups chlorinated, which is necessary to avoid reaction of the composition with chlorofluorocarbon refrigerants.
U.S. Pat. No. 4,200,543 was issued to Liston, et al in Apr. 29, 1980. This patent teaches an internal combustion engine crankcase oil comprising various sulfur-containing anti-oxidants, oil-soluble chlorinated hydrocarbons containing at least six carbon atoms, and an oil-soluble zinc salt. At Column 2, lines 35-45, the patent suggests that the oil-soluble chlorinated hydrocarbon alone does not provide any of the anti-oxidant properties necessary in crankcase oil. The use of chlorinated paraffin waxes is suggested at Column 4, lines 18-23.
In short, references which disclose refrigeration oils have not disclosed chlorinated hydrocarbon lubricant additives at all, and references disclosing chlorinated hydrocarbon additives do not contemplate their use in refrigeration oils. The prior art teaches away from the addition of chlorinated hydrocarbons which lack fluorine substitution to a compressor charge.